Oxygen Vacancy Formation Energy Research Articles

First-principle investigation the initial oxidation of methane on Pd doped LaCo0.2Fe0.8O3-δ anode surfaces of solid oxide fuel cells

Initial oxidation of methane (CH4) is essential for subsequent oxidation reactions on anode surfaces of solid oxide fuel cells (SOFCs). Here first principle method was employed to investigate the initial oxidation mechanism of CH4 on Pd doped LaCo0.2Fe0.8O3-δ (LCF) anode. Results show that Pd-doping decreases formation energies of surface oxygen vacancy. The adsorption ability of CH4 molecules is also improved on perfect LCF surface by Pd-doping. Dissociation barriers of CH4 on LCF surfaces are greatly decreased with min value of 1.14 eV by Pd-doping and surface oxygen vacancy compared to those on perfect and defective LCF surfaces (min values of 1.76 and 1.34 eV, respectively). Results of Bader charges and bond lengths of CH4 (or CH3) and OH show that the initial oxidation of CH4 molecules is namely the oxidation of dissociated H atoms from CH4 molecules. And higher valences of surface metal atoms interacted with CH4 molecules mean the lower dissociation barriers of CH4 molecules.

Highly Dispersed Mn-Doped Ceria Supported on N-Doped Carbon Nanotubes for Enhanced Oxygen Reduction Reaction.

The weak adsorption of oxygen on transition metal oxide catalysts limits the improvement of their electrocatalytic oxygen reduction reaction (ORR) performance. Herein, a dopamine-assisted method is developed to prepare Mn-doped ceria supported on nitrogen-doped carbon nanotubes (Mn-Ce-NCNTs). The morphology, dispersion of Mn-doped ceria, composition, and oxygen vacancies of the as-prepared catalysts were analyzed using various technologies. The results show that Mn-doped ceria was formed and highly dispersed on NCNTs, on which oxygen vacancies are abundant. The as-prepared Mn-Ce-NCNTs exhibit a high ORR performance, on which the average electron transfer number is 3.86 and the current density is 24.4% higher than that of commercial 20 wt % Pt/C. The peak power density of Mn-Ce-NCNTs is 68.1 mW cm-2 at the current density of 138.9 mA cm-2 for a Zn-air battery, which is close to that of 20 wt % Pt/C (69.4 mW cm-2 at 106.1 mA cm-2). Density functional theory (DFT) calculations show that the oxygen vacancy formation energies of Mn-doped CeO2(111) and pure CeO2(111) are -0.55 and 2.14 eV, respectively. Meanwhile, compared with undoped CeO2(111) (-0.02 eV), Mn-doped CeO2(111) easily adsorbs oxygen with the oxygen adsorption energy of only -0.68 eV. This work provides insights into the synergetic effect of Mn-doped ceria for facilitating oxygen adsorption and enhancing ORR performance.

Co, Ni and Cu-doped Ca2Fe2O5-based oxygen carriers for enhanced chemical looping hydrogen production

Oxygen carrier determines the output characteristics of the chemical looping cycle reaction and is a key factor affecting the chemical looping hydrogen production (CLH) process. In this work, the effect of different dopants (Co, Ni and Cu) on Ca2Fe2O5 brownmillerite-type oxygen carriers and the feasibility of low doping were investigated in an attempt to improve CO conversion and hydrogen yield in the CLH reaction. The redox activity of the transition metal doped oxygen carriers was significantly enhanced. The fuel conversion of CaFeNi was increased to 1.29 times. The average hydrogen yield of CaFeCo was as high as 102.20 mL/g, which was 1.58 times that of CaFe. In addition, density functional theory calculations show that metal-doped Ca2Fe2O5 reduced the energy of oxygen vacancy formation, but they bore a significant energy barrier in the formation of hydrogen molecules. These findings may provide ideas for the modification of oxygen carriers for the CLH process.

Stabilized Nickel-Rich oxide cathode by the confining effect of Nb lattice anchoring and epitaxial shielding layer

Ni-rich LiNixCoyMn1−x−yO2 cathodes attract growing attention for high energy density but still face great challenges in terms of cyclic lifespan and thermal stability issues. The structural degradation is primarily caused by the increased oxygen vacancy and lattice oxygen loss, especially at high temperatures. Here, we develop an anchoring-confining strategy to rivet lattice oxygen and inhibit the formation and migration of oxygen vacancy by constructing LiNbO3 & LiF epitaxial layer and Nb5+ lattice doping within LiNi0.92Co0.055Mn0.025O2 (NCM92) cathode. The optimized NCM-FN material exhibits excellent stability with retenion of 93 % after 200 cycles at 1C supassing the pristine one (68.7 %), conspicuous high-temperature capacity retention rate (81.6 % vs. 49.5 %) and superior reversible capacity of 165 mAh/g at 5C. In particular, it even possessed superior thermal safety pushing thermal runaway temperature to 223.65 °C. In-situ X-ray diffraction (XRD) result indicates that Nb5+ lattice substitution coupled with LiNbO3 & LiF epitaxial layer alleviates the irreversibility of H2-H3 phase transition, thus stabilizing the layered structure. Furthermore, the LiNbO3 & LiF epitaxial layer, as both a physical shielding layer and ionic conductive layer, protects interface structural integrity and simultaneously promotes Li+ diffusion. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) results demonstrate that the formation and propagation of oxygen vacancy within NCM-FN material is significantly inhibited. DFT calculation results reveal that Nb5+ introduction can increase the formation energy of oxygen vacancies and inhibit outward migration of active oxygen Oα- (α < 2) to stabilize layer structure by tuning the breaking energy barrier of nearby metal-O bonds. This work not only demonstrates the design of advanced Ni-rich layered cathodes but also underscores the importance of stabilized lattice oxygen for advanced Ni-rich cathodes.

First principles calculation and experimental study of Ln0.125Sr0.875Co0.875Ta0.125O3-δ(Ln = La, Sm, and Nd) as potential cathode materials for intermediate-temperature solid oxide fuel cells

Solid oxide fuel cells (SOFCs), as important energy equipment, have excellent characteristics, including low pollution and high catalytic activity. The cathode, which is the key component of an SOFC, plays a vital role in practical applications. Herein, we study the properties of Ln0.125Sr0.875Co0.875Ta0.125O3-δ (Ln = La, Sm, and Nd, abbreviated as LSCT, SSCT, and NSCT, respectively) cathode materials both theoretically and experimentally. The conductivity of LnSCT gradually decreased with decreasing Ln3+ ionic radius. Density of states (DOS) analysis indicated that LSCT has the highest conductivity owing to the band center of Co 3d being closer to O 1s. Density functional theory (DFT) calculations showed that the SSCT sample has the lowest oxygen vacancy formation energy, which facilitated the formation of oxygen vacancies. The binding energy results show that SSCT and NSCT have relatively good structural stability compared to LSCT. The polarization impedance values of LSCT, SSCT, and NSCT at 700 °C are 0.105, 0.069, and 0.304 Ω cm2, respectively. The CO2 sensitivity of LSCT, SSCT, and NSCT was evaluated by calculating the CO2 adsorption energy and performing impedance tests under different CO2 concentrations. These results indicate that LSCT and SSCT have better CO2 tolerance than NSCT. At 700 °C, for Ln = La, Sm, and Nd, the maximum power of NiCu-SDC/SDC/LSGM/LnSCT electrolyte-supported fuel cell reached 430, 462, and 382 mW cm−2, respectively. These findings provide a reference for the future design and development of SOFCs cathode material.

Reverse Atom Capture on Perovskite Surface Enabling Robust and Efficient Cathode for Protonic Ceramic Fuel Cells.

Protonic ceramic fuel cells (PCFCs) hold potential for sustainable energy conversion, yet their widespread application is hindered by the sluggish kinetics and inferior stability of cathode materials. Here, a facile and efficient reverse atom capture technique is developed to manipulate the surface chemistry of PrBa0.5Sr0.5Co1.5Fe0.5O5+ δ (PBSCF) cathode for PCFCs. This method successfully captures segregated Ba and Sr cations on the PBSCF surface using W species, creating a (Ba/Sr)(Co/Fe/W)O3- δ (BSCFW)@PBSCF heterostructure. Benefiting from enhanced kinetics of proton-involved oxygen reduction reaction and strengthened chemical stability, the single cell using the optimized 2W-PBSCF cathode demonstrates an exceptional peak power density of 1.32W cm-2 at 650°C and maintains durable performance for 240h. Theoretical calculations unveil that the BSCFW perovskite delivers lower oxygen vacancy formation energy, hydration energy, and proton transfer energy compared to the PBSCF perovskite. This protocol offers new insights into advanced atom capture techniques for sustainable energy infrastructures.

Construction of core–shell structured CrOx/NiCoxO4 catalyst for low temperature catalytic oxidation of toluene: Understanding the reactivity promotion mechanism of the core–shell interactions

Bimetallic-based spinels are potential materials for toluene oxidation ascribing to their remarkable stability and oxidation activity. However, the insufficient toluene adsorption capacity and limited reactive oxygen species severely restrict their low-temperature catalytic reactivity. This study reports a facile two-step solvothermal strategy for the synthesis of core–shell structured CrOx/NiCoxO4 catalyst, which exhibits excellent toluene oxidation performance with T50 and T90 values of 187 and 218 °C, respectively, and the toluene conversion remains above 90 % at 218 °C for 20 h. The in-situ DRIFTs indicate that the oxidation of toluene to CO2 and H2O follows Mars-van Krevelen (MvK) mechanism, and the rate limiting step is the oxidation of maleic anhydride. The strong interaction between core NiCo2O4 and shell Cr2O3 regulates the morphology of Cr2O3 from particles to porous flocculent structure, which increases the porosity of catalyst and promotes the adsorption of toluene for further oxidation. Moreover, the interaction promotes the charge transfer from NiCo2O4 to Cr2O3, which increases the adsorbed oxygen species contents and the redox capability of the catalyst. A further density functional theory (DFT) calculation confirms that the core NiCo2O4 is the main active component, where the oxygen vacancy formation energy of NiCo2O4 and Cr2O3 decrease from 2.43 and 3.85 eV to 0.31 and 1.52 eV, while the toluene adsorption energy decrease from −0.04 and −0.94 eV to −5.29, and −4.48 eV, respectively, which evidently demonstrates that the formation of core–shell structured CrOx/NiCoxO4 would significantly promote the adsorption and oxidation of toluene, thereby exhibiting excellent low temperature toluene oxidation reactivity.

Precise modulation of surface lattice to reinforce structural stability of high-nickel layered oxide cathode by hafnium gradient doping

The quest for high-energy lithium-ion batteries has intensified interest in high-nickel layered oxide cathode materials, while the rise in nickel content adversely impacts structural stability and cycling performance. Herein, Hafnium (Hf) anchored at nickel (Ni) site precisely modulates the surface crystal lattice of high-nickel cathode (LiNi0.9Co0.05Mn0.05O2, NCM90) that is confirmed by Rietveld refinement of neutron powder diffraction. Notably, the strengthened structural stability thanks to Hf gradient doping is firmly substantiated by in-situ X-ray diffraction and in-situ X-ray adsorption spectroscopy. This enhancement can be ascribed to the substantial atomic mass of Hf and large radius of Hf4+, facilitating the minimization of potential alterations of interlayer or intralayer. The intensified Hf-O bond significantly increases the formation energy of oxygen vacancies and efficiently restrains the detrimental Li+/Ni2+ disorder, thereby mitigating lattice oxygen loss and enhancing both cycling and thermal stability of high-nickel cathode. Consequently, the 0.3 % Hf-doping cathode exhibits considerable improvement in electrochemical performance, delivering superior capacity retention of 95.0% after 100 cycles at 1C (1 C = 200 mA g−1) and 83.9 % after 500 cycles at 1C/5C in the voltage range of 3.0∼4.3 V. This work highlights the benefits of precise modulation strategy for high-nickel cathodes, offering a viable approach to enhance structural stability and electrochemical performance of high-nickel cathodes.

Stabilizing Lattice Oxygen through Mn Doping in NiCo2O4-δ Spinel Electrocatalysts for Efficient and Durable Acid Oxygen Evolution.

Design the electrocatalysts without noble metal is still a challenge for oxygen evolution reaction (OER) in acid media. Herein, we reported the manganese (Mn) doping method to decrease the concentration of oxygen vacancy (VO) and form the Mn-O structure adjacent octahedral sites in spinel NiCo2O4-δ (NiMn1.5Co3O4-δ), which highly enhanced the activity and stability of spinel NiCo2O4-δ with a low overpotential (η) of 280 mV at j=10 mA cm-2 and long-term stability of 80 h in acid media. The isotopic labelling experiment based on differential electrochemical mass spectrometry (DEMS) clearly demonstrated the lattice oxygen in NiMn1.5Co3O4-δ is more stable due to strong Mn-O bond and shows synergetic adsorbate evolution mechanism (SAEM) for acid OER. Density functional theory (DFT) calculations reveal highly increased oxygen vacancy formation energy (EVO) of NiCo2O4-δ after Mn doping. More importantly, the highly hydrogen bonding between Mn-O and *OOH adsorbed on adjacent Co octahedral sites promote the formation of *OO from *OOH due to the greatly enhanced charge density of O in Mn substituted sites.

High-Performance Ir1/CeO2 Single-Atom Catalyst for the Oxidation of Toluene.

The elimination of toluene is an obligatory target with increasing VOC emission in recent years. This study successfully prepared a single-atom Ir catalyst (Ir1/CeO2) by a simple incipient wetness impregnation method, confirmed by in situ CO DRIFTS and AC-HAADF-STEM. Compared to the cluster Ir catalyst (Ir/CeO2-C), Ir1/CeO2 exhibited excellent catalytic performance, stability, and water resistance for the oxidation of toluene. By Raman, H2-TPR, O2-TPD, and XPS experiments, abundant oxygen defects and a unique Ir3+-Ov-Ce3+ structure were formed for the Ir1/CeO2 sample because it had a lower oxygen vacancy formation energy. Furthermore, the DFT results revealed that the Ir1/CeO2 sample had a lower ring-opening energy barrier and adsorption energy of the ring-opening products, which was the rate-determining step for the oxidation of toluene. This work provides instructive insights into the construction of Ir/CeO2 catalysts for the highly efficient removal of VOCs.

High-performance Ti-doped strontium cobaltite perovskites as oxygen electrodes in solid oxide cells

Oxygen electrodes play a vital role in realizing high-performance solid oxide cells (SOCs) with high roundtrip efficiency, large-scale capacity, and long-term stability energy storage. This paper constructs Ti-doped strontium cobaltite perovskites (SrCo1-xTixO3-δ, SCTx, x = 0.2, 0.3, 0.4, 0.5) as newly stable oxygen electrodes for SOCs. The changes of oxygen vacancy in SCTx with Ti-doped concentration are investigated by X-ray photoelectron spectroscopy (XPS). The results show that the content of oxygen vacancy decreases with the enrichment of Ti doping. The area-specific resistance (ASR) of the symmetrical cell with SrCo0.8Ti0.2O3-δ (SCT2) electrode is only 0.013 Ω cm2 at 850 °C in air. The single cell with SCT2 oxygen electrode achieves the peak power density of 1.313 W cm−2 at 850 °C under humidified H2 conditions in fuel cells mode, and the current density reaches 2.95 A cm−2 under an electrolytic voltage of 1.9 V at 850 °C for CO2 electrolysis. The Density functional theory (DFT) calculations confirm that the oxygen vacancy formation energy is the lowest when the ratio of Ti to Co is 2:8, verifying the superior property of SCT2. This study comes up with a creation for developing high-stability and high-activity oxygen electrode materials that can be used for energy storage systems.

Optimizing the CeO2-MnO2 interface via H2O2 etching for surface lattice oxygen activation in the plasma catalytic degradation of trimethylamine

Trimethylamine (TMA) is a nitrogen-containing malodorous gas that is toxic and hazardous to humans. Plasma catalysis is a promising technique for removing low-concentration malodorous gases. CeO2/MnO2 nanowires with different Ce–Mn contact interfaces prepared by impregnation, physical mixing, and H2O2 etching were investigated for TMA degradation in a plasma catalytic system. The CMO-H sample prepared by H2O2 etching achieved a removal efficiency of 100% at 98 J/L, demonstrating the highest activity. Characterization revealed that H2O2 etching led to the uniform formation of CeO2 nanoparticles on MnO2, promoting the transfer of electrons between Ce and Mn species. Surface lattice oxygen and high-valent manganese were confirmed to be the main active species, consistent with the Mars van Krevelen mechanism. Density functional theory calculations confirmed that the CMO-H sample exhibited the lowest oxygen vacancy formation energy. In situ plasma diffuse reflection infrared transform spectroscopy analysis and gas chromatography-mass spectrometry results showed the possible degradation pathway of TMA. In summary, the H2O2 etching process optimized CeO2-MnO2 interactions and improved the utilization of lattice oxygen active sites, enhancing the catalytic degradation of TMA and providing new insights into the design of an efficient plasma catalytic system for environmental remediation.

Application of lattice expansion effect in SrCoO3 based cathodes by Ba doping with elevated electrochemical performances for low-temperature solid oxide fuel cells

Developing excellent-performance cathode materials is an inevitable and challenging obstacle in the process of developing practical solid oxide fuel cells, especially in low temperature range. In this paper, we introduce barium into the premium SrCoO3-based cathodes and research its consequent effect in the oxygen reduction reaction process. It is observed that the barium dopant could expand the lattice, produce more oxygen vacancies and at some extent reduce the thermal expansion coefficient of parent perovskite, which results from the expanded free space for oxygen migration and weakened Co–O bond by Ba doping. The polarization resistances of single cells with Sr1-xBaxCo0.8Sc0.1Nb0.05Ti0.05O3-δ cathodes (x = 0, 0.2 and 0.5, defined as SCSNTi, SB0.2CSNTi and SB0.5CSNTi, correspondingly) are 0.038, 0.025 and 0.016 Ω cm2 at 600 °C, respectively, and corresponding peak power density of 0.852, 1.054 and 1.217 W cm−2. The SB0.5CSNTi cathode is selected and it stably operates for 200 h at 550 °C. And it also exhibits excellent performance when CH4 is used as fuel and good stability for 100 h at 600 °C. First principle calculations prove that the Ba doping effectively reduces the oxygen vacancy formation energy and oxygen migration barrier. This work proves that the lattice expansion effect is an effective strategy for accelerating the oxygen exchange rate and designing high-performance cathode materials.

Efficient catalytic combustion of propane at low temperature based on ignition effect caused by amorphous atomic-layer Pt clusters

Developing highly active catalysts for hydrocarbon combustion at low temperatures is paramount but yet challenging. The crystal form of carrier and the dispersion degree of active species have great influence on propane combustion catalysts, but its internal mechanism is still unclear. In this study, the amorphous atomic-layer Pt clusters (AL) and Pt single atoms (SA) on TiO2 with various crystal phases were prepared and used as propane combustion catalysts, where the as-synthesized Pt/a-TiO2 catalyst with atomic-layer Pt clusters exhibited better catalytic performance. The Pt/a-TiO2-AL could achieve a 90 % propane conversion (T90) at 230 °C, with the highest reaction rate (39.57 × 10−7 mol g−1 s−1) and TOF value (7.72 × 10−2 s−1) at 240 °C. Kinetic studies showed that oxygen had a lower inhibitory effect on Pt/a-TiO2-AL compared to that on the Pt/p-TiO2-AL and Pt/r-TiO2-AL catalysts; simultaneously, the Pt/a-TiO2-AL catalyst presented lower apparent activation energy compared with Pt/a-TiO2-SA. DFT results showed that atomic-layer Pt clusters on TiO2 had the lower formation energy of oxygen vacancy than Pt single atoms due to the synergistic effect between adjacent exposed Pt atoms in the fully exposed atomic-layer Pt clusters, which had a higher activation capacity for oxygen and thus accelerated propane combustion through the ignition effect (rapid activation of oxygen and rapid combustion of propane). Our primary results provide a promising approach for the creation of high-efficiency Pt-based catalysts, specifically tailored for the catalytic combustion of volatile organic compounds (VOCs).

Stabilizing Lattice Oxygen through Mn Doping in NiCo2O4−d Spinel Electrocatalysts for Efficient and Durable Acid Oxygen Evolution

Design the electrocatalysts without noble metal is still a challenge for oxygen evolution reaction (OER) in acid media. Herein, we reported the manganese doping method to decrease the concentration of oxygen vacancy (Vo) and form the Mn−O structure adjacent octahedral sites in spinel NiCo2O4−δ (NiMn1.5Co3O4−δ), which highly enhanced the activity and stability of spinel NiCo2O4−δ with a low overpotential (η) of 280 mV at j = 10 mA cm−2 and long‐term stability of 80 h in acid media. The isotopic labelling experiment based on differential electrochemical mass spectrometry (DEMS) clearly demonstrated the lattice oxygen in NiMn1.5Co3O4−δ is more stable due to strong Mn‐O bond and synergetic adsorbate evolution mechanism (SAEM) for acid OER. Density functional theory (DFT) calculations reveal highly increased oxygen vacancy formation energy (EVO) of NiCo2O4−δ after Mn doping. More importantly, the highly hydrogen bonding between Mn−O and *OOH adsorbed on adjacent Co octahedral sites promote the formation of *OO from *OOH due to the greatly enhanced charge density of O in Mn substituted sites.

Enhancing Oxygen Reduction Activity and CO2 Tolerance by a Bismuth Doping Strategy for Solid Oxide Fuel Cell Cathodes

AbstractLayered perovskite related oxides, LnBaCo2O5+δ (Ln = rare‐earth element) are potential ceramic cathodes for intermediate temperature solid oxide fuel cells. Herein, a simple way to tune the performance of NdBaCo2O5+δ (NBC) perovskite as a cathode by doping the Co‐site with bismuth cation is reported. Compared with the parent oxide, the obtained stabilized double perovskites NdBaCo2−xBixO5+δ (x = 0.1 and 0.2) show a much improved electrocatalytic activity, achieving area‐specific resistance of 0.268, 0.107 and 0.152 Ω cm2 at 700 °C in air for NBC, x = 0.1, and 0.2, respectively. Density functional theory results demonstrate that bismuth doping effectively reduces the formation energy of oxygen vacancies. Moreover, the bismuth doping of NdBaCo2−xBixO5+δ cathode is much more robust against CO2 than that of NBC cathode. This work indicates that bismuth doping in the B‐site of LnBaCo2O5+δ may be a highly attractive strategy for the future development of cathode materials.

ABO3 perovskite catalyst screening for chemical looping methane partial oxidation from descriptor-based microkinetic analysis

DFT calculations and descriptor-based microkinetic analysis have been performed to screen ABO3 perovskite catalysts for methane partial oxidation. The scaling relations indicate the adsorption energies of H@O and CH3@B have the capability of representing the energetics of methane oxidation, and bulk oxygen vacancy formation energy is identified to be a better single descriptor of the kinetics. The resultant volcano-shaped plot shows the catalytic activity varies in the order LaMnO3 > LaFeO3 > LaCoO3 ≈ LaCrO3, which agrees with the experimental findings and thus validates our theoretical predications. By screening 667 combinations of A- and B-cations based on electron neutrality, structural tolerance factors, and experimental verification, 77 ABO3 have been identified to be stable. Of them, SrRuO3, SmRhO3, LaIrO3, NdRhO3, and BaOsO3 are located at the summit of the volcano, which also exhibit satisfactory CO selectivity and enhanced carbon resistance compared to LaFeO3, and may act as the oxygen carrier candidates.

Circumventing the Theoretical Scaling Relation Limit for the Oxygen Evolution Reaction.

Transition metal hydr(oxy)oxides (TMHs) are considered efficient electrocatalysts for the oxygen evolution reaction (OER) under alkaline conditions. Toward identification of potential descriptors to circumvent the scaling relation limit for the OER, first-principles calculations were used to quantify the effects on the overpotential of different s (Mg), p (Al), and d (Ti, V, Cr, Fe, Co, Sc, and Zn) electron dopants in Ni-based TMHs. Both the adsorbate evolution mechanism (AEM) and the lattice oxygen-mediated mechanism (LOM) were examined. The results demonstrate that the formation energy of oxygen vacancies (EVO) is strongly affected by the chemical nature of the dopants. A linear relationship is identified between EVO and the free energy difference for the oxygen-oxygen coupling. A descriptor could be employed to discriminate whether the LOM is energetically favored over the AEM. These findings fill existing gaps in appropriate yet computationally light descriptors for direct identification between the AEM and LOM.

Binary Li/Na tungstates modified Mg6MnO8 as redox catalysts for enhanced performance of chemical looping oxidative dehydrogenation of ethane

The present investigation delves into the utilization of Mg6MnO8 modified with binary Li2WO4 and Na2WO4 tungstates as oxygen carriers for the chemical looping oxidative dehydrogenation (CL-ODH) of ethane. The Mg6MnO8-LiNaW2 oxygen carrier demonstrates remarkable performance, achieving up to 77.7 % ethane conversion, 86.5 % ethylene selectivity, and 67.2 % ethylene yield. HRTEM-EDS reveals the formation of a molten binary tungstates layer covering the solid Mg6MnO8 substrate. The molten binary tungstates layer effectively modulates the release of lattice oxygen in a step-wise manner during ODH reactions. XPS analysis reveals that the doping of Li/Na binary tungstates inhibits the formation of OH−/CO32− and Mn4+ species, thus preventing the deep oxidation of ethylene. The Mg6MnO8-LiNaW2 sample maintains stable reactivity and surface morphology throughout 20 redox cycles. DFT calculations further indicate that the modification with Li/Na binary tungstates promotes electron accumulation around the local environment of the Me-O bond, thereby reducing the formation energy (Eo) of oxygen vacancy in Mg6MnO8 and improving the oxygen vacancy concentration within the bulk of the oxygen carriers. The superior ethylene selectivity of the Mg6MnO8-LiNaW2 oxygen carrier can be attributed to the higher oxygen diffusion capability in the bulk of the Mg6MnO8 core, coupled with the lower oxygen transport rate through the molten tungstates layer.

Unveiling the confinement and interface effect on low temperature degradation of toluene over mesoporous zeolite encapsulated Pt-CeO2 catalyst

The efficient degradation of volatile organic compounds (VOCs) at low temperatures is urgently needed due to the serious environmental and health hazards they pose. While precious metal-based catalysts offer excellent performance, their application is limited by high-temperature sintering and aggregation. Therefore, inhibiting the migration and aggregation of precious metals during the reaction process can effectively improve their utilization and alleviate catalyst deactivation. In this study, a novel encapsulated catalyst (Pt-CeO@meso-S1) containing Pt-CeO2 interfaces was constructed using mesoporous-rich zeolite as a shell layer and applied to the catalytic oxidation of toluene. The introduction of CeO2 constructed a Pt-CeO2 active interface that promoted the low-temperature degradation of toluene, achieving complete oxidation of toluene at 160 ℃. The crystalline phase transition strategy enhanced the specific surface area, improving the dispersion of platinum and facilitating the construction of the Pt-CeO2 interface. The zeolite shell and mesoporous pores effectively confined/stabilized the Pt-CeO2 active components and inhibited platinum sintering, resulting in outstanding water resistance and high-temperature stability. DFT calculations demonstrated that the presence of the Pt-CeO2 active interfaces reduced oxygen vacancy formation energy and facilitated gas-phase oxygen activation. DFT calculations demonstrated that the presence of the Pt-CeO2 active interfaces reduces the oxygen vacancy formation energy and boosts the activation of gas-phase oxygen. The Mars-van-Krevelen (MvK) mechanism governing toluene degradation over Pt-CeO2@meso-S1 was revealed by in situ DRIFTS. This work provides a promising candidate for industrial high-performance catalytic removal of VOCs at low temperatures.